Sugar ester preparation and purification



SUGAR ESTER PREPARATION AND PURIFICATION No Drawing. Filed Jan;r4,,19's9 seaNo saasr 12 Claims. Cl. 260-234 a The present applicationis directed to. a method of sugar ester purification, more specificallya method for puritying partial and complete esters of various sugars.

In the past, compounds of the sugar ester type have been manufactured bythe use of solvent systems which are toxic. Furthermore these systemspresent a serious danger of contamination when the ultimate product isto be used for human consumption. As a result, elaborate and expensiverefining means are required to insure that the sugar esters produced donot carry any substantial amounts of toxic solvents with them. 7 r r 7It is among the objects of this invention to provide a method forpreparation and purification of sugar esters which will enable theformation of partially as well as completely esterified products.

It is also among the objectsof this invention to provide a' means forpurification of sugar esters both partial and complete, which willobviate any danger of contaminationwith toxic substances.

It. is further among the objects of this invention to provide a means ofpurifying sugar esters which will be suitable for use in the preparationof products for human consumption.

It is still further among the objects of this invention to provide. amethod of purification of sugar esters which yields a clean, sharpseparation of the desired products from the undesired by-products.

.In practicing this invention, a sugar, preferably sucrose, is dissolvedor suspended in an aqueous alkaline medium. An amount of acid chloride.corresponding to the desired degree of esterification is then,addedslowly. Preferably the acid chloride should be at least 98% puresince the presence of any substantial amount of phosphorous trichlorideor of phosphorous acid will cause the formation of undesired phosphatesrather than the sugar ester sought, and the yield is low; also theseparation of the ester from the other constituents of the mass andpurification thereof becomes more difficult. Furthermore, if free fattyacids are present, larger quantities of soap are produced and thereaction rate and efiiciency is reduced.

The alkaline aqueous suspension or solution of sugar should bemaintained preferably at pH 9 to ll. However, the reaction will proceedas long as the pH of the sugar solution is on the alkaline side. At a pHof greater than 11, the efiiciency of the reaction goes down and moresoap is formed. It the pH is permitted to drop below 7, a verysubstantial increase in the amount of soap or free fatty acid results.

i The reaction is carried out at a temperature below 65 C. and above thefreezing point of the acid chloride used. Preferably the reactiontemperature should be below 40 to 45;C. as the yield drops oif abovethis temperature range, and the agitation is continued throughout thereaction. As a general rule, the process is conducted at the lowestpermissible temperature based on the fluidityof the reactants.

In carrying out this process, the sugar solution is placed in a mixingdevice capable of giving turbulent agitation.

- Patented Aug. 9, 1960 2 Y An appropriate acid chloride is added,together with sufficient sodium hydroxide and/or other alkali tomaintain. the desired pH. This addition is made slowly and at a pointwhere thorough turbulent mixing is always maintained. The sugar solutionas a whole is always in excess over the acid chloride as a whole.However, at the point of entry of the acid chloride into the sugarsolution, there will be some local acidification. Rapid and adequateagitation keeps this to a minimum and effectively converts the medium toan alkaline one in a matter of seconds, ensuring that the reactionproceeds in the right direction. Since the reaction is exothermic, it isdesirable to cool the reactants preferably by means of a water jacket orcracked ice. If the acid chloride is present in excess, substantialquantities of free fatty acids are formed. which will usuallyprecipitate out and hence impair the efliciency of the reaction.

In other words, it is important that a combination ofv temperaturecontrol, rapid and turbulent mixing, alkalinity and slow addition ofacid chloride and the alkali be maintained. Once this reaction has takenplace and the crude ester is formed, the reaction mass is mixed forabout an hour and then it is ready for processing whenthe last traces ofacid chloride have reacted. The resultant product is in the formof'a'slurry,""of which approximately 20% constitutes the desired sugarester.

Concentration and purification of the crude product is obtained by firstwashing the mixture with hot brine, pref-. erably around 20% solution atto C. This causes the slurry to split into two layers; the upper layercontains the desired sugar ester plus the soap formed as well as somewater and salt. The lower layer is primarily the brine and unreactedsugar. The layers are then separated and the top layer rewashed andre-separated as described before.

The ester, soap layer is then drained and the vacuum dried to avirtually anhydrous conditionj this operation is important for thesubsequent separation of sugar ester from the soap present in thereaction mass. The dry ester, soap mixture is then extracted with hotacetoner This dissolves out the sugar ester which is soluble in acetonebut does not dissolve the undesired soap impurity. Consequently it isthen only necessary to distill oil the acetone to recover the pureproduct. 1

It should be noted that for the best operation of this purificationprocess it is very important that the crude.

' ester soap mixture be dried to a virtually anhydrous con-1 dition.Alternatively, if substantial quantities of waterare present, then whenextracted with hot acetone thewater will also dissolve in the acetoneand carry some soap with it. Under these conditions, it becomesnecessary to very carefullydistill off the acetone until the water.separates out as a second layer carrying with it the soap. At this pointthe material must be permitted tostand so that all the water and soapwill goout of solution. The? water layer is drawn OE and the remainderis then filtered v r and the acetone redistilled to obtain the pureester. 3

The purified compounds find substantial'use as emulsi-" has in the food,pharmaceutical, medicinal and cosm etic industries. In the food industryit is suitable forluse in margarine, shortening, ice'creams and manyallied uses as in candy coatings, baked goods, etc. They areemulsifiers, anti-spattering agents, emulsion stabiliz e foamingaerating agents, gloss additives, and suspendi and thickening agents.Also in the pharmaceutical field larly, these esters have manyindustrial uses in such' fields. as textiles, leather, paper making, andothers. j j] The following specific examples of this invention areintended to be illustrative only and not toindi cat limitations to beimposed thereon;

Example 1 In a vessel capable of good mixing and turbulent agitation,there is charged 350 lbs. of sucrose and 200 lbs. of water. To thehomogeneous solution while under turbulent agitation, there is slowlyadded a 50% sodium hydroxide solution, together with 310 lbs. ofstearoyl chloride. The sodium hydroxide is added at such a rate as willmaintain the pH between 9 and 10. The additions take approximately 4 to5 hours and mixing is maintained for one hour after all addition hasbeen completed. A thick paste containing the crude ester results. Thisproduct is then washed with sodium chloride solution at a temperature ofapproximately 80 to 90 C. The sugar ester and soap formed separate fromthe unreacted sugar and alkaline water. The brine solution layer isdrawn off and discarded. This cycle is repeated to get a betterseparation of the ester.

The ester layer is then dried slowly under vacuum until completely dryand then extracted with hot acetone at a temperature close to theboiling point of the acetone. This effects the separation of the puresugar ester from the soap formed as a by-product of the initialreaction. The extraction is repeated until the bulk of the ester hasbeen recovered. The acetone is then flashed off to recover the puresugar ester, which can either be ground to a powder, flaked off on aroll or recovered in any of the ordinary forms.

Example 2 350 grams of sugar were dissolved in 200 grams of water in amixing vessel equipped with efficient agitation and cooled to about 25C. While maintaining agitation and cooling, a small amount of a 20% NaOHsolution was added to bring the pH to about 8, after which 280 grams ofpalmitoyl chloride together with NaOH solution was introduced slowly tomaintain a pH of about 9-l0, over a period of about 34 hours.

The temperature at the start was about 2025 C. and gradually rose to3035 C. at the height of the reaction and gradually dropped to 30 C.when the reaction was completed. The batch was agitated one hour afterall the additions were made and the traces of free acid chloride presentwere given the opportunity to react and become neutralized.

The thick, syrupy, white, precipitate which resulted from the aboveinitial esterification reaction was then transferred to a wash tankwhere the entire batch was given a hot brine wash (15 NaCl solution at80-90" 0.). Equal volumes were used for convenience and rapid washing.However, smaller volumes can be used and one, two, or three such washescan be given to ensure the elimination of the unreacted sugar from thebatch. The concentration of the brine solution may vary and even solidNaCl may be used to separate layers.

The brine wash separated the batch into two layers. The top layercontained a curd of the sucrose ester and any soap which was formed as aside reaction. The bottom layer contained the water, alkali, salt, andespecially the unreacted sugar in the batch. In order to preventformation of dark colors, bad odors and flavors on decomposition ofsugar, it is important to wash out the sugar as thoroughly as possibleto ensure a final product of a high degree of purity, quality in tasteand flavor and odor.

When the brine washed crude sucrose ester was obtained free fromunreacted sugar, it was placed in a kettle equipped with agitation, heat(indirect) and vacuum. While under agitation the batch was slowly heatedand vacuum applied to draw off all the water present in the batch, afterwhich the batch was cooled while still being agitated and the vacuumkept on until the temperature was reduced to 50 C. to ensure good colorto the product. The vacuum was gradualy broken and about 3500 grams ofhot acetone gradually introduced into the batch and extracted. The hotacetone .4 slurry containing the sugar ester in solution and the soapand salts in suspension were filtered, maintained at the sametemperatures, where the press cake of salts and soap built up while theclear acetone solution containing the sugar ester filtered through andcollected in a receiver. The acetone was distilled from the sugar estersolution and recycled as long as necessary to ensure that all the sugarester had been extracted from the press cake. The final residue,obtained after the acetone is distilled from the receiving flash, wasthe pure sugar ester.

Example 3 Follow Example 2 up to the washing with sodium chloride. Afterthe brine washing of the crude sucrose ester the curd was immediatelyput through the pressure leaf filter press and pressed out to as dry acake as possible. The press cake was then extracted with the hot acetoneas before. The extracted material contained, beside the sugar ester, thesoap impurity which is soluble in the aqueous acetone. As the acetonewas evaporated, an aqeuous layer formed. This aqueous layer containedmost of the soap which is not soluble in anhydrous alcohol. The waterlayer was drawn 01f from the bottom of the vessel and the acetonesolution concentrated to the point where no more water layer formed. Itwas then filtered through a fine filter to ensure the elimination of anyfine suspended particles of soap. The concentrate was now completlyfreed from acetone to yield the sugar ester free from impurities.

Example 4 11,000 grams of sucrose was dissolved in 6,000 grams of waterand cooled to 10-12 C.

To the above sugar solution, while maintaining vigorous agitation andtemperatures below 20 C., a solution of 640 grams of sodium hydroxidedissolved in 2,200 grams of water was added in a slow stream to maintainthe pH of the sugar solution at 9-10. At the same time 2,800 grams ofpalmitoyl chloride (99% purity) was gradually added to the sugarsolution over the course of 3 hours. The temperature of the batch neverexceeded 18 C.

When the last of the palmitoyl chloride was added, the batch wasimmediately brine washed with saturated brine solution at 60-65 C. Thebrine solution was separated and the remaining washed sugar esterextracted with acetone. The extracted acetone solution was distilled toeliminate the acetone, then filtered to recover the pure sugar ester asa white solid. The yield of pure sucrose ester was 2,050 grams.

Although the invention was described in connect-ion with severalspecific embodiments thereof, certain changes and variations in thedetails may be introduced. By varying the molar ratios of the acidchloride, sugar esters ranging from monoto octa-sucrose esters may beprepared. Mixed esters of sugars may be produced by following the aboveprocedures. The use of high purity acid chlorides is important.

Other solvents than acetone are suitable, such as mono alcohols having2-4 carbon atoms, alkylene dichlorides wherein the alkylene group has 24carbon atoms, carbon tetrachloride, chloroform, hexane, and benzol. Theymay be characterized as volatile organic solvents for sugar esters butnot solvents for soaps. The alkyl radical of the esters may have from 2.to 24 carbon atoms, but preferably they have from 12 to 18 carbon atomsfor many applications; saturated and unsaturated fatty acid chloridesare contemplated. The products range from viscous liquids to lightcolored friable solids.

Important to the invention are the following conditions: (1) the use ofa pure acid chloride, (2) a low temperature of reaction, (3) maintaininga moderately alkaline pH, (4) efficient agitation during the reaction,and (5) the purification of the crude ester by brine, and (6) thenextraction with an organic solvent.

Various sugars may be used as starting materials for the operation.While acetone has been found, up to the present time, to be the mosteffective solvent for the purpose, the other solvents named above areusable with lesser efiiciency; the solvents should be volatile attemperatures below the decomposition point of the products. It ispreferred to operate at the lower range of the temperatures' set forth,but the higher temperatures are also operative; while as high as 65 C.has been found efiective, better results are obtained in working asclose to 0 C. as is practical, but the temperature should be above themelting point of the acid chloride used. The reaction being exothermic,cooling the reaction mass is advisable. In the reaction it is preferableto have an excess of sugar present to minimize the formation of freefatty acids. Allowing the reaction mass to stand for at least one hourafter the reaction is apparently complete insures that no traces of acidchloride remain.

If the acid chloride does not find suitable media to react and form thesucrose ester it will hydrolize and form free fatty acid or else ifthere is suflicient alkali, form soap. Both these side reactions must bekept to a minimum. In order to do this the most suitable conditions forester formation are maintained, i.e. adequate mixing, low concentrationsof acid chloride at any given moment, low concentration of alkali at anygiven moment, and reaction at the lowest temperature possible at whichthe sugar, the acid chloride and the alkali are still fluid.

We claim:

1. The method of preparing sugar esters comprising dissolving sugar inwater, making the solution alkaline, slowly adding organic acid chloridewhile turbulently agitating and maintaining the mixture alkaline wherebycrude sugar ester is formed, maintaining the temperature of the reactionbelow 65 C. and at which the acid chloride is still fluid, washing saidcrude ester with a solution of a salt which does not change thealkalinity of the mixture and is adapted to cause precipitation of esterand soap from aqueous solutions and permitting said mixture to separateinto an ester-soap layer and an electrolyte-sugar layer, removing saidelectrolyte-sugar layer, drying said ester-soap layer, extracting theester with a ketone, and recovering substantially pure ester from saidketone.

2. The method of preparing sugar esters according to claim 1 wherein thereaction is carried out at a temperature of about 25 -45 C.

3. The method of preparation of sugar esters according to claim 1wherein the ketone containing the ester is filtered to remove suspendedsalts and soap and then distilled to recover the pure ester.

4. The method of preparation of sugar esters according to claim 1wherein the pH of the reaction mixture is 7-11.

5. The method of preparation of sugar esters according to claim 1wherein the pH of the reaction mixture is 9-10.

6. The method of preparation of sugar esters according to claim 1wherein the molecular ratio of sugar to acid chloride is 3 :1 to 1:3.

7. The method of preparation of sugar esters according to claim 1wherein the acid chloride is substantially free from phosphoruscompounds.

8. The method of preparing sugar esters comprising dissolving sugar inwater, making the solution alkaline, slowly adding organic acid chlorideWhile turbulently agitating and maintaining the mixture alkaline wherebycrude sugar ester is formed, maintaining the temperature of the reactionbelow C. and at which the acid chloride is still fluid, washing saidcrude ester with a solution of a salt which does not change thealkalinity of the mixture and is adapted to cause precipitation of esterand soap from aqueous solutions and permitting said mixture to separateinto an ester-soap layer and an electrolyte-sugar layer, removing saidelectrolyte-sugar layer, drying said ester-soap layer, extracting theester with an organic solvent which is volatile at temperatures belowthe decomposition point of the product, and recovering substantiallypure ester from said solvent.

9. The method of preparation of sugar esters according to claim 8wherein said solvent is taken from the class consisting of mono-alcoholshaving 2-4 carbon atoms and hydrocarbons having 2-7 carbon atoms.

10. The method of preparation of sugar esters according to claim 8wherein said solvent is taken from the class consisting of chlorinatedhydrocarbons having 2-4 carbon atoms and l-4 chlorine atoms.

11. The method of preparing sugar esters comprising dissolving sugar inwater, making the solution alkaline, slowly adding organic acid chloridewhile turbulently agitating and maintaining the mixture alkaline wherebycrude sugar ester is formed, maintaining the temperature of the reactionbelow 65 C. and at which the acid chloride is still fluid, washing saidcrude ester with a solution of a salt which does not change thealkalinity of the mixture and is adapted to cause precipitation of esterand soap from aqueous solutions and permitting said mixture to separateinto an ester-soap layer and an electrolyte-sugar layer, removing saidelectrolyte-sugar layer, extracting the ester with an organic solventwhich is volatile at temperatures below the decomposition point of theproduct, and recovering substantially pure ester from said solvent.

12. The method of preparation of sugar esters according to claim 11wherein the temperature of the ester forming reaction is below 20 C.

References Cited in the file of this patent UNITED STATES PATENTS2,024,036 Funaoka Dec. 10, 1935 2,052,029 Harris Aug. 25, 1936 2,602,789Schwartz July 8, 1952

1. THE METHOD OF PREPARING SUGAR ESTERS COMPRISING DISSOLVING SUGAR INWATER, MAKING THE SOLUTION ALKALINE, SLOWLY ADDING ORGANIC ACID CHLORIDEWHILE TURBULENTLY AGITATING AND MAINTAINING THE MIXTURE ALKALINE WHEREBYCRUDE SUGAR ESTER IF FORMED, MAINTAINING THE TEMPERATURE OF THE REACTIONBELOW 65*C. AND AT WHICH THE ACID CHLORIDE IS STILL FLUID, WASHING SAIDCRUDE ESTER WITH A SOLUTION OF A SALT WHICH DOES NOT CHANGE THEALKALINITY OF THE MIXTURE AND IS ADAPTED TO CAUSE PRECIPITATION OF ESTERAND SOAP FROM AQUEOUS SOLUTIONS AND PERMITTING SAID MIXTURE TO SEPARATEINTO AN ESTER-SOAP LAYER AND AN ELECTROLYTE-SUGAR LAYER, REMOVING SAIDELECTROLYTE-SUGAR LAYER, DRYING SAID ESTER-SOAP LAYER, EXTRACTING THEESTER WITH A KETONE, AND RECOVERING SUBSTANTIALLY PURE ESTER FROM SAIDKETONE.